Field of the Invention
The invention relates to a data transmission system including two or more data processing units that are connected to one another through a bus having two lines. Furthermore, the invention is directed to a data transmission method.
German Published, Non-Prosecuted Patent Application DE 196 22 685 A1, corresponding to U.S. Pat. No. 6,052,635 to Swart et al., discloses a data transmission system having at least two data processing units that are connected to one another through a bus having two lines and used in a passenger protection system of a motor vehicle. In the Swart system, a control device is connected to an ignition driver circuit through a bus having two lines. Between the two bus lines, a direct voltage is present for supplying the ignition driver circuit with voltage on which is modulated the data signal transmitted by amplitude modulation.
In general, such data transmission systems are at risk from short circuits because the data transmission can no longer be reliably guaranteed should one of the bus lines come into conductive contact with a component that is at a fixed potential, for example, with ground potential, on-board voltage, or another fixed potential as a result of a fault. Such conductive contacting can occur due to vibrations that occur strongly in the motor vehicle, whirring-through, or defectiveness of the insulation etc. In such a case, it is not only the data transmission that can be impaired in a safety-critical manner but possibly also the bus driver or drivers can be damaged due to the high short circuit current that can interfere with or render impossible any subsequent data communication after the short circuit has been eliminated or has disappeared. In such a case, the driver also needs to be exchanged.
It is accordingly an object of the invention to provide a data transmission system, particularly, in a motor vehicle, and a data transmission method, that overcomes the hereinafore-mentioned disadvantages of the heretofore-known methods and devices of this general type and that has improved short-circuit resistance.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a data transmission system including a bus having two lines with different nominal potentials applied to the two lines at least during data transmission, at least two data processing units connected to one another through the bus, a controller generating data modulated onto at least one of the nominal potentials as modulation signals, at least one driver for generating the modulation signals to be transmitted, the at least one driver connected to the two lines, and a short-circuit detector device for detecting a short circuit of one of the two lines, the short-circuit detector device applying a nominal potential originally provided for a short-circuited one of the two lines to another one of the two lines not short-circuited dependent upon a detection of a short circuit.
In the invention, the occurrence of a short circuit of one or both bus lines is actively checked and when short circuit currents or voltages occur, corresponding counter measures are initiated. Preferably, the nominal potentials of the two bus lines are switched over after a short circuit has been detected so that, for example, the line previously carrying positive potential is now at zero potential or low potential and the line previously at zero potential or low potential is switched over to the high potential. If, for example, the bus line previously at high potential shows a short circuit to ground or a low potential value, the switching over of the bus line potentials can have the effect that essentially the same difference voltage between the bus lines is received at the receiver end and the configuration amplitude modulation percentage can be essentially retained in the data transmission. Such occurs because the bus line that was previously at or near zero potential assumes a high potential after the polarity switch-over so that the potential difference with respect to the other bus line that is short circuited to ground potential or low potential largely remains guaranteed. The polarity switch-over of the two bus lines in the case of a short circuit can make it possible not only to retain reliable data transmission but, if necessary, also allow continuous voltage feeding to be maintained if the bus lines are used not only for data transmission but also for direct-current feeding of the connected data processing units (see e.g., Swart).
In accordance with another feature of the invention, there is provided a short-circuit detector device exchanging the nominal potentials of the two lines with one another dependent upon the detection of the short circuit.
In accordance with a further feature of the invention, the short-circuit detector device switches off one of the drivers associated with the short-circuited one of the two lines dependent upon the detection of the short circuit. When a short circuit is detected, the driver of the short-circuited bus line can also be disabled, if necessary, so that overloading and damage to the driver due to excessive short-circuit currents is avoided.
In accordance with an added feature of the invention, there is provided a short-circuit detector device for detecting a short circuit of one of the two lines, the short-circuit detector device amplifying a swing of the modulation signals on one of the two lines not short-circuited dependent upon a detection of a short circuit.
In accordance with an additional feature of the invention, the at least one driver is two drivers respectively connected to the two lines, and the control device controls, after a switch-off of a first of two drivers due to a short circuit, a second of the two drivers such that the second driver impresses a voltage change of twice an amplitude of an undisturbed case of the modulation signals on a respective one of the two lines associated with the second driver for data transmission.
In accordance with yet another feature of the invention, the controller generates data modulated onto only one of the nominal potentials as modulation signals, at least one driver connected to the two lines generates the modulation signals to be transmitted, and a short-circuit detector device detects a short circuit of one of the two lines, the short-circuit detector device modulating modulation signals onto the nominal potential of another of the two lines dependent upon a detection of a short circuit of the one of the two lines transmitting the modulation signals.
In accordance with yet a further feature of the invention, at least one driver is two drivers respectively connected to the two lines, a line voltage detection device checks a potential of a short-circuited one of the two lines, and the controller controls, dependent upon a line voltage, at least one of a switch-over of the nominal potentials and a switching-off of at least one of the two drivers.
In accordance with yet an added feature of the invention, the line voltage detection device checks a potential of the two lines.
In accordance with yet an additional feature of the invention, the at least one driver is two drivers operating synchronously in an undisturbed case and respectively providing half an amplitude modulation swing and each of the two lines is connected to one of the two drivers.
In accordance with again another feature of the invention, at least one of the at least two data processing units evaluates a voltage difference between the two lines for data detection.
With the objects of the invention in view, there is also provided a method for transmitting data in a data transmission system having at least two data processing units coupled to one another through a bus having two lines carrying modulation signals and drivers connected to the bus, including the steps of applying different nominal potentials to each of the two lines at least during data transmission, checking the two lines with regard to an occurrence of a short circuit, and applying, in a case of a short circuit of one of the two lines, a nominal potential originally provided for the short-circuited line to another of the two lines not short-circuited.
In accordance with again a further mode of the invention, the nominal potentials of the lines are exchanged with one another in the case of a short circuit.
In accordance with again an added mode of the invention, a driver associated with the short-circuited line is switched off in the case of a short circuit.
In accordance with again an additional mode of the invention, whether or not one of the drivers is operating in a current-limiting mode is checked and, if so, the one driver is switched off and the potential existing on one of the two lines associated with the one driver is subsequently checked.
In accordance with still another mode of the invention, the potential existing on the other one of the two lines is checked.
In accordance with still a further mode of the invention, the one driver is kept switched off if the potential of the one line associated with the one driver or the potential of the other of the two lines deviates from a nominal potential of the respective line by less than a given value, preferably, by less than 50%.
In accordance with still an added mode of the invention, another switch-over of a polarity of the bus is prevented after the polarity of the bus has been switched over once and the short-circuit current still occurs.
In accordance with still an additional mode of the invention, after the driver has been switched off, a driver still operating is controlled to generate a voltage change swing of twice a magnitude of an undisturbed case of the modulation signals on a respective one of the two lines.
With the objects of the invention in view, there is also provided a method for transmitting data in a data transmission system having at least two data processing units coupled to one another through a bus having two lines carrying modulation signals and drivers connected to the bus, including the steps of applying different nominal potentials to the two lines at least during data transmission, modulating the modulation signals onto at least one of the nominal potentials, checking the two lines with regard to an occurrence of a short circuit, and increasing a swing of the modulation signals on one of the two lines not short-circuited in a case of the short circuit.
In accordance with still another mode of the invention the swing of the modulation signals is doubled.
With the objects of the invention in view, there is also provided a method for transmitting data in a data transmission system having at least two data processing units coupled to one another through a bus having two lines carrying modulation signals and drivers connected to the bus, including the steps of applying different nominal potentials to the two lines at least during data transmission, modulating the modulation signals onto only one of the nominal potentials of one of the two lines, checking the two lines with regard to an occurrence of a short circuit, and in a case of the short circuit of the one line transmitting the modulation signals, modulating the modulation signals onto the nominal potential of the other one of the two lines.
The data transmission system according to the invention can be constructed such that in the short-circuit-free case, only one of the bus lines is subjected to amplitude modulation for data transmission whereas the other bus line remains at a constant potential. It is only after a short circuit occurs on the previously amplitude-modulated bus line, that switching-over to the other bus line for amplitude modulation would occur. Preferably, however, the bus driver system is configured to be balanced and synchronously modulates the nominal line voltages of, for example, +10 V and 0 V so that the intended modulation amplitude change is equally distributed to both lines. Should the amplitude modulation be configured with a modulation percentage of 50%, one line is switched over, for example, between +10 V and +7.5 V whereas the other line is switched between 0 V and +2.5 V synchronously thereto. Thus, the receiver sees difference voltage fluctuations of 10 V and 5 V between the two bus lines. In such a system, if one of the two line drivers must be switched off because of a short circuit of the associated bus line, the driver of the other functioning bus line is preferably switched over such that it now generates twice the voltage swing. If, for example, the +10 V bus line is short circuited to ground, it is not only the other bus line that is switched from previously 0 V to +10 V but the driver is also driven such that it performs an amplitude modulation of between +10 V and +5 V. The receiver thus receives the same amplitude modulation percentage as in the undisturbed case. The effect improves the data transmission reliability even further. The doubling of the amplitude swing of the one driver after disabling the driver of the other bus line can also be provided in a case in which no previous potential switch-over of the bus line potentials has taken place. Such can be the case if, for example, the bus line previously operated at the nominal potential of 0 V should experience a permanent short circuit to ground. In such a case, naturally, the potential switch-over does not take place but the amplitude swing of the drivers of the other bus line that is at a high level is still preferably doubled.
The data transmission system described can be generally used for data transmission of any type of data and in any systems but is preferably used in the motor vehicle field, for example, in a motor vehicle passenger protection system for transmitting data between a central control device and sensors and/or igniter driver circuits, or in an immobilizer control system or the like.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a data transmission system, particularly, in a motor vehicle, and a data transmission method, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.